I have never thought of elves as being immortal, practical or otherwise. True, they did not age and die as mortal men, but they were subject to other causes of death. Elves were no doubt aware of this mortality. As such, extended families and clans would be means of insuring survival of not only a family lineage but elf-kind as a whole. Counting the names of Elvish sons and daughters is not an accurate way to determine birth rate. In our own history, often only the name of son or daughter of particular importance were were recorded.

: There is also the strange paradox of the events of the Silmarillion, which Tolkien wanted to present as a sort of invented mythology. This is how they are presented in LOTR, as events of a mythical past. Though to some of the characters of LOTR such as Galadriel, Celeborn, Cirdan etc these events were those of their own memories and therefore most definitely non-mythical. Tolkien would have been better advised to have made his elves long-lived compared to humans but certainly not immortal.

The position of Gladriel, Celeborn etc. is similar to that of people in the American west of the 1870's. Many of them lived to see their history become myth in the hands of authors and motion picuture writers. Likewise, many of todays youth look back at the First World War and the Great Depression as some distant and remote event. However, many people still remember those times and events as part of their life. Seeing events of your life become history or myth has always been with us, and will continue.